Welcome to SI. I'm sorry you qualify for membership, but since you do, I'n glad you found us.
First, NC means no new hurts. My reco is to stay away from the ap. He's not the problem.
More important, you write a story that seems to say you've done some rugsweeping and some going back over the same ground again and again.
Being betrayed is traumatic. It brings with it immense anger, grief, fear, shame, etc. IMO, you've got to process those feelings out of your body. To stay together, your WS needs to know you're angry, grief-stricken, scared, ashamed, etc.
You've also got to explicitly define what you want from your M. You've got to figure out what will satisfy you, and she has to figure out what will satisfy her. And your W has to change from betrayer to good partner.
Since this has been going on for a long time, my reco is to find a good IC, someone who will help you recover, whether that means R or D.
Also. the thread https://survivinginfidelity.com/topics/660527/for-those-who-found-out-years-later-part-2/ might help you.
You can heal, even though the A was so long ago. It takes courage and effort, but asking your W if she had sex with the guy says pretty clearly that you courage. And holding all this in for so long indicates you've got a lot of energy that you can use for your healing.
You can get through this and thrive.
[This message edited by SI Staff at 4:53 PM, Thursday, May 1st]